Collapsible play yard

ABSTRACT

A locking mechanism comprises: a hub movable between a raised and a lowered position and a pair of structures, pivotally mounted to a common bracket. Sector gears engage each other rotate in unison. A locking assembly mounted upon the common bracket moves between a locked position preventing rotation of said structures and a released position allows rotating of said structures. At least two rods are pivotally joined to one of said structures. When the lock button is unlocked, and the hub is lifted, the rods are moved together to be substantially parallel, and when the hub is lowered, the gears rotate and the rods are pushed away from each other until the rods lie substantially in a common plane, enabling, the locking button to be moved to its locked position to prevent movement of the hub from the lowered position.

FIELD OF INVENTION

The field of the invention generally is collapsible play yards or playpens and more particularly to releasable locking mechanisms for such collapsible devices.

BACKGROUND

A collapsible play yard provides a portable but stable structure in which a small child can play and sleep. The essential features for such a structure is that it be (1) lightweight enough to carry by one person, (2) easy to set up, and (3) stable enough to safely support the child. An example of a portable play yard is shown in U.S. Pat. No. 4,811,437 to Dillner et al.

The Dillner play yard uses a center hub about which the uprights of the play yard are pivoted. The hub employed in the Dillner play yard is a complex device and the need exists for a simpler center hub design.

Similarly, Dillner provides a play yard having upper rails comprised of several moving parts and a need exists for a simpler upper rail design.

SUMMARY

The present invention is characterized by a locking mechanism for a foldable enclosure, which comprises: a) a hub movable between a raised position and a lowered position, comprising i) a pair of structures, each rotatably mounted upon pivots extending through a common bracket wherein sector gears of each structure meshingly engage each other causing the structures to rotate in unison about their respective pivots; and ii) a locking assembly movably mounted upon the common bracket between a locked position that prevents rotation of said structures about their respective axes and a released position that allows rotation of said structures their respective axes; and iii) at least two rods each pivotally joined to an associated one of said structures. When a lock button of the locking mechanism is moved to an unlocked position, the hub is free to be lifted toward the raised position, whereby the rods are moved together to be aligned substantially in parallel. When the hub is pushed into the lowered position from the raised position, the cooperating structures rotate about their pivots whereby the rods are moved away from each other until the rods lie substantially in a common plane, which constitutes the erected position. When the rods reach the erected position, the locking button is automatically moved to its locked position which prevents accidental movement of the hub from the lowered position (wherein the play yard is erected) to the raised position (wherein the play yard is collapsed).

BRIEF DESCRIPTION OF THE DRAWING(S)

FIG. 1 is an isometric view of the erected play yard.

FIG. 2 is an isometric view of the collapsed play yard.

FIGS. 3, 3 a, and 3 b are isometric views that illustrate the sequence of moving the frame between the erected and the collapsed position in FIG. 3 b.

FIG. 4 is a side elevation view of the frame of FIG. 3.

FIG. 5 is a fragmentary view showing the center hub of FIG. 3 in greater detail.

FIG. 6 is a side elevational view of the center hub of FIG. 5.

FIG. 7 is a cross section of the center hub looking in the direction of arrows 7-7 of FIG. 6.

FIG. 8 is a cross section of the center hub of FIG. 6 looking in the direction of arrows 8-8 of FIG. 7.

FIG. 9 is an enlarged cross section of the center hub looking in the direction of arrows 9-9 of FIG. 8.

FIG. 10 is an isometric fragmentary view illustrating the center hub in a collapsed condition.

FIG. 11 is a cross section of the center hub looking in the direction of arrows 11-11 of FIG. 10.

FIG. 12 is a cross section of the center hub looking in the direction of arrows 12-12 of FIG. 11.

FIG. 13 is an exploded view of the center hub, and FIG. 13 a is an isolated view of the centerpiece of the hub of FIG. 13.

FIG. 14 illustrates a locking mechanism for locking the rails of the play yard of the present invention.

FIG. 15 is a cross section in the direction of arrows 15-15 of FIG. 14.

FIG. 16 is a cross section in the direction of arrows 16-16 of FIG. 15.

FIG. 17 illustrates the release button of the locking mechanism of FIG. 14.

FIG. 18 is a cross section in the direction of the arrows 18-18 of FIG. 17.

FIG. 19 is a cross section in the direction of arrows 19-19 of FIG. 18.

FIG. 20 is an exploded view of the locking mechanism of FIG. 17 and FIG. 20 a is a fragmentary view of the interior of the bracket in FIG. 20.

FIG. 21 is an exploded view of an upper corner assembly for the play yard of the present invention.

FIG. 22 is a cross section in the direction of arrows 22-22 of FIG. 21.

FIG. 23 illustrates a lower corner assembly for the play yard of the present invention.

FIG. 24 is a cross section in the direction of arrows of 24-24 of FIG. 23.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT(S)

FIG. 1 shows a fully assembled and erected play yard 10, which has a flexible enclosure 14 that covers a foldable frame 20 formed of rigid components (shown in FIGS. 2 and 3). The enclosure 14 is mounted upon the frame 20 by means of extending upper horizontal rails 22 through hollow horizontal sleeves 16 and also extending vertical rails 24 through vertical sleeves 17. A removable mattress floor 18, placed upon a floor of the enclosure 14 provides a soft surface for child to sleep or play on.

FIG. 2 shows the play yard 10′ folded onto itself and enclosed within the folded mattress 18′. Edge 18 a′ has strips which may be Velcro® strips that cooperate with complementary Velcro® pieces on end 18 b′. FIGS. 3, 3 a, and 3 b show the steps in folding the frame 20. For purposes of simplicity, FIGS. 3, 3 a, and 3 b omit the flexible enclosure 12 and mattress floor 18.

Starting from the fully erected frame shown in FIG. 3, the frame 20 is collapsed onto itself as shown in FIG. 3 b by releasing locking mechanisms 200 and unlocking and raising the center hub 50. The releasable locking mechanisms 200 are each joined to a cooperating pair of upper frame rods 28, 28. The upper frame rods 28 are each hingedly joined at an inner end to an associated locking mechanism 200 and at an outer end to an arm of an associated upper corner piece 30.

Once the releasable center hub 50 and locking mechanisms 200 are unlocked, raising the center hub 50 draws the four base frame rods 32 upward. The base frame rods are each pivotally mounted at one end to an associated structure 52, 52 forming part of the center hub 50, and at the other end to an associated one of the lower corner pieces 34. As the base frame rods 32 are drawn upward (FIG. 3 a), the vertical rails 18 draw inward towards the rising hub 50, and the releasable locking mechanisms 200 move downward.

FIG. 3 b shows the hub 50 raised to its lifted position in which the frame 20′ is folded onto itself and is thus fully collapsed for ease of storage/transport. In this position, the vertical rails 18, upper frame rods 28, and base frame rods 32 are substantially parallel to one another.

FIG. 3 also shows optional lower support rods 36 that are pivotally mounted to brackets 37 which, in turn, are joined to the base frame rods 32 and have their inner ends pivotally mounted to supplemental feet 38. Feet 38 are optionally mounted to an associated pair of lower support rods 36 and have base portions 38 a that provide additional support for the floor of the play yard. The base portions 38 a of feet 38, the bottom of bracket 56 and the bottoms of lower corner pieces 34 are arranged to engage a planar floor or other supporting surface to stably support the playard.

FIGS. 5-13 show a more detailed view of the center hub 50; of those, FIG. 13 shows the component parts of the hub 50 most clearly. The hub 50 comprises a pair of sector gear structures 52, a central piece 54, bracket 56 for supporting piece 54 and structures 52, and a movably mounted locking button assembly 58. Pivot pins 66 secure the structures 52 to the bracket 56 and central piece 54. Each structure 52 rotates about its associated pivot pin; as the structures rotate, teeth 62 on each of the sector gear structures 52 meshingly engage one another, to provide a smooth and yet positive rotation of the structures 52 that raise and lower the hub 50, assuring that the rods simultaneously swing through like angles when raised/lowered.

Structures 52 each have an integral hollow support arm 64 for receiving overlapping ends of an associated pair of base frame rods 32. The ends of rods 32 each have a cutout 32 a so that they closely overlap one another and can pivot independent of to one another when held to an associated hollow arm 64 by pivot pin 60. When the center hub 50 is pulled upward in the direction of arrows, the vertical rails 18 are drawn inward due to movement of the ends of base frame rods 32, mounted to lower brackets 34, which move towards each other.

Each structure 52 is comprised of a pair of spaced apart gear sectors 53 a, 53 b. Sector gears 53 a, 53 a of the structures 52 are diagonally opposed to one another and gear sectors 53 b, 53 b are likewise diagonally opposed to one another. Gear sectors 53 a, 53 a each have a shoulder 79 and the gear sectors 53 b each have a shoulder 78-78. The shoulders 78-78 are each closer to a vertical axis which coincides with arrow A in FIG. 13 such that the shoulders 78, 78 are each closer to said central axis. Diagonally aligned sector gears 53 a, 53 a mesh with an associated diagonally aligned sector gear 53 b, 53 b.

The locking member 58 is held against axial movement within the central piece 54 by bolt 68 and nut 70 while being capable of rotating about the vertical axis. A tab 72 is integrally joined to locking member 58. Distance D1 between ends 72 a-72 b is greater than the distance D2 between ends 72 c-72 d. Tab 72 is positioned beneath side guides 74, 74. The opposite ends 72 c, 72 d of tab 72 are engaged by shoulders 78-78 when the hub 50 is lowered to the erected position to prevent hub 50 from being accidentally unlocked and to thereby secure the locking button 58 in a locked position (shown in FIGS. 5-9). A torsion spring 76 biases the locking member 58 to rotate in the counter-clockwise direction shown by arrow B to move the tab 72 to the locked position when the hub is in the erected position. Note that the shoulders 79-79 provide sufficient clearance to permit the tab to move to the locked position.

With the hub 50 in the lowered position, the spring-biased tab 72 rotates counter-clockwise until ends 72 a, 72 b each engage an associated shoulder 78, 78. Once opposing surfaces 72 c, 72 d of tab 72 each engage an associated shoulder 78, the gear structures 52 cannot rotate in either direction about pins 66 because tab 72 is prevented from rotating by shoulders 78, 78, retaining the tab in a locked position. This is best seen in FIG. 6. The locking surfaces 78 a, 78 a, 79 a, 79 a of the gears 53 a, 53 a, 53 b, 53 b, abut the underside 72 c of tab 72 preventing the hub assembly 50 from being lifted. The underside of bracket 56 rests in a supporting surface when the play yard is fully erected (see FIG. 4).

To release the gear structures 52 so they can rotate, the locking member is turned clockwise, preferably by gripping curved wire handle 80. The gear sector structures 52 include diagonally opposed clearance shoulders 79, 79 that provide sufficient clearance for tab 72, allowing the tab 72 to rotate in the clockwise direction. When the tab 72 is so rotated, opposite ends 72 c, 72 d of tab 72 each enter into one of the gap spaces 82 between the opposing pairs of gear sectors wheels 53 a-53 b. Once the ends 72 c, 72 d of tab 72 each enter into one of the gap spaces 82, the blocking surfaces 79 a, 79 a, 78 a, 78 a are clear of tab 72, enabling structures 52, 52 to rotate freely about their associated pivots 66 allowing hub 50 to be lifted to its raised position shown in FIGS. 10-12.

As is best seen in FIG. 12, although the tab 72 is urged counter-clockwise because of the spring bias, the tab 72 is prevented from rotating by the interior sidewalls of the gear sectors 53 a, 53 a and thus the tab is retained within the gap 82. Upon lowering to the erected position, tab 72 is clear of the shoulders 79, 79 as well as surfaces 78 a, 78 a, 79 a, 79 a (see FIG. 3), enabling the spring 76 to urge the tab 72 toward the locked position shown in FIGS. 5-9 without the need for manually rotating the locking button 58 into the locked position.

FIGS. 14-20 show one of the upper horizontal rail locking mechanisms 200. FIGS. 14-16 show the locking mechanism 200 in its locked position, while FIGS. 17-19 show the unlocked position.

The locking mechanism 200 comprises mounting bracket 202, a locking wedge 204, a locking spring 206, a push button 208, and a cover 210. The bracket 202 optionally has a pin 212 and a spacer/bushing 214 that provide structural support: the bushing 214 fills the gap between opposing walls W1-W2 of bracket 202, and thus inhibits their movement towards or away from each other when under stress.

The push button 208 and locking wedge 204 engage one another in a threaded, snap-fit, or other secure arrangement. The arm 205 of wedge 204 extends through spring 206, which spring has one end 206 a which presses against the push button 208 and an end 206 b secured to the projection 203 of bracket of 202. When assembled as shown in FIG. 15, the spring 206 biases the push button 208 in the direction of arrow C and away from bracket 202. This bias force also urges the wedge portion 207 of the locking wedge 204 in the direction of arrow C. Depressing the push button 208 against the force of spring 206, compresses the spring 206 and drives the wedge portion 207 into the hollow cover 210 attached to the bracket 202, as shown in FIG. 18.

In the locked position (FIGS. 14-17), the wedge portion 207 engages inserts 29 provided in upper frame rails 28. Inserts 29 and rails 28 are pivotally mounted to bracket 202 by a pin 216 which prevents inserts 29 from moving along their axes and further prevents inserts 29 from rotation about their axes. The inserts 29 each have a cutout 218 that engages an associated end of the wedge portion 207 to achieve this locked position. To prevent inadvertent unlocking, the cutouts 218 each preferably have a small integral protrusion 220 that engages an associated recess 222 in wedge 207.

To unlock the upper horizontal rails for folding, the protrusion 220 and the recess 222 must first be disengaged so that the push button 208 can be depressed. Prior to this disengagement, the push button 208 cannot be depressed because of the engagement of the protrusion 220 and recess 222. In practice, this disengagement is accomplished by lifting the bracket 202 slightly, which swings each protrusion 220 upward and away from its associated recess 222. To unlock the mechanism 200, the push button 208 is pressed in to by a distance sufficient to assure that the wedge 207 is clear of the path of movement of the cutout 218 as each rod 28 rotates about its associated pin 216.

FIGS. 21 and 22 show an upper corner piece 30 that engages tapered outer ends 302 of associated upper frame rods 28. Each rod 28 fits into an associated slot 30 b and rotates about a pin 304 extending through opening 307 each in arm 302 and openings 308 in corner piece 30. Corner piece 30 minimizes the possibility of trapping a finger in the corner piece 30, by using the narrow tapered end 302 and cooperating narrow slot 306.

FIGS. 23 and 24 show one of the lower corner pieces 34. The lower support rod 32 rotates about pivot pin 400 within the opening 402 within the lower corner piece 34. It should be noted that the tapered end/narrow slot design for the upper corner piece may also be incorporated into the lower corner piece 34.

Vertical arm 24 is force-fitted into bore 403 of corner piece 34. Arm 24 has an integral tab 24 a which is normally biased in an outward radical direction and which snap-fits against an upper edge 404 a in opening 404 in corner piece 34 when the rod 24 is pushed into bore 403 by an amount sufficient to clear edge 404 a of opening 404. Rod 24 may be removed from lower corner piece 34 by pressing tab 24 a inwardly sufficient to clear edge 404 a. Foot 405 is preferably provided with a “tread” to provide a non-slip grip with a surface supporting the play yard. 

1. A locking mechanism for foldable enclosure, comprising: a) a hub movable between a raised position and a lowered position, comprising: i) a pair of structures, each pivotally mounted to a common bracket wherein sector gears of each structure engage each other causing the structures to rotate in unison about their respective axes; and ii) a locking assembly movably mounted upon the common bracket between a locked position that prevents rotation of said structures about their respective axes and an unlocked position that allows rotation of said structures about their respective axes; iii) at least two rods each pivotally joined to an associated one of said structures; b) wherein when a button of the locking assembly is operated to move the locking assembly to the unlocked position, the structures are released, enabling the hub to be lifted toward the raised position, and outer ends of the rods to move together so as to be substantially parallel, and when the hub, when unlocked, is pushed toward the lowered position from the raised position, said structures rotate about their axes and the outer ends of the rods are pushed away from each other until the rods lie substantially in a common plane; and c) wherein when the rods lie in said common plane, the locking button is moved to its locked position which prevents accidental movement of the hub from the lowered position to the raised position.
 2. The locking mechanism of claim 1 further comprising: d) an upper frame having an open position wherein the upper frame forms a rigid perimeter around a first area and a collapsed position wherein the upper frame forms a perimeter around a second area; e) vertical rails joining the upper frame and the rods; and f) a flexible enclosure joined to the upper frame and vertical rails; g) wherein when the hub is in the lowered position and the upper frame is in the open position, the flexible enclosure forms a flexible wall and floor that encloses and defines a volume with an open top.
 3. The locking mechanism of claim 1 further comprising a mattress that rests on the rods when the hub is in the lowered position.
 4. The locking mechanism of claim 1 wherein the locking button is rotatable between the unlocked position and the locked position in which a tab on the locking button engages first shoulders on each of said structures to retain said tab in a locked position.
 5. The locking mechanism of claim 1 wherein the locking button is rotatable between the unlocked position and the locked position in which a tab on the locking button engages second shoulders on each of said structures to retain said structures in a locked position.
 6. The locking mechanism of claim 1 wherein the hub further comprises a foot that engages a planar surface when the center hub is in the lowered position.
 7. The locking mechanism of claim 6 further comprising a plurality of feet connected to the rods that engage a planar surface when the center hub is in the lowered position.
 8. The locking mechanism of claim 2 wherein the upper frame further comprises four collapsible sides, each side including two upper frame rods hingedly joined at one end to an upper corner piece and hingedly joined at an opposite end to a releasable locking mechanism that releaseably secures the two upper frame rods so that the two upper frame rods are aligned along a substantially straight line.
 9. The locking mechanism of claim 8 wherein when each of the two upper frame rods on each of the four collapsible sides is aligned along its respective straight line, the upper frame is in the open position.
 10. The locking mechanism of claim 8 wherein the relasable locking mechanism comprises a means for releasably locking the two frame rods.
 11. The locking mechanism of claim 2 wherein the upper frame has four upper corner members that form substantially square corners for the upper frame when the upper frame is in the open position.
 12. The locking mechanism of claim 1 wherein the rods are hingedly connected at their second end to lower corner members that form substantially square corners when the hub is in the lowered position.
 13. The locking mechanism of claim 1 further including base support rods rotatably joined to the rods at a first end thereof and a supplemental foot at a second end thereof.
 14. A center hub for a collapsible play yard comprising: a) a pair of geared structures, each pivotally mounted on a common support member and spaced apart so that the geared structures engage each other; and b) a locking button attached to the center piece movable between a locked position that prevents rotation of the toothed structures about their axes and a released position that allows rotation of the geared structures.
 15. An upper rail of a play yard comprising two upper frame rods hingedly joined at one end to an upper corner piece and hingedly joined at an opposite end to a releasable locking mechanism that releasably secures the two frame rods so that the two frame rods are aligned along a substantially straight line, the locking mechanism comprising a spring-biased button attached to a wedge that engages cutouts in the opposite ends of the upper frame rods.
 16. The upper rail of claim 15 wherein the wedge has a groove therein and the cutout has a protrusion thereon, wherein the protrusion and the groove matingly engage to prevent disengagement of the cutout and wedge.
 17. The upper rail of claim 15 wherein raising the locking mechanism disengages the protrusion from the groove, thus allowing the cutout and wedge to also disengage.
 18. An upper corner piece for a play yard comprising a slot for receiving a tapered end of a support rail and a pivot point around which said rail rotates within said slot.
 19. A gear mechanism for a play yard comprising i) a pair of structures, each pivotally mounted to a common bracket wherein sector gears of each structure engage each other causing the structures to rotate in unison about their respective axes; and b) wherein when the hub is lifted toward the raised position, the structures rotate about their axes and each sector gear engages the other.
 20. A gear mechanism for a play yard comprising i) a pair of structures, each rotatably mounted upon pivots extending through a common bracket wherein two spaced apart pairs of sector gears of each structure engage each other causing the structures to rotate in unison about their respective axes; and b) wherein when the hub is lifted toward the raised position, the structures rotate about their axes and each sector gear engages the other.
 21. A foldable enclosure, comprising: a) a hub movable between a raised position and a lowered position, comprising: i) a pair of structures, each rotatably mounted upon pivots extending through a common bracket wherein sector gears of each structure engage each other causing the structures to rotate in unison about their respective axes; and ii) a means for locking mounted upon the common bracket that moves between a locked position that prevents rotation of said structures about their respective axes and a released position that allows rotation of said structures their respective axes; iii) at least two rods each pivotally joined to an associated one of said structures; b) an upper frame having an open position wherein the upper frame forms a rigid perimeter around a first area and a collapsed position wherein the upper frame forms a perimeter around a second area; c) vertical rails joining the upper frame and the rods; and d) a flexible enclosure joined to the upper frame and vertical rails; e) wherein when the lock button is moved to an upper unlocked position, and the hub is lifted toward the raised position, the rods are moved together to be substantially parallel, and when the hub is pushed into the lowered position from the raised position, the toothed structures rotate about their axes and the rods are pushed away from each other until the rods are substantially in planar alignment; and f) wherein when the rods are in planar alignment, the locking button can be moved to its locked position which prevents accidental movement of the hub from the lowered position to the raised position. g) wherein when the hub is in the lowered position and the upper frame is in the open position, the flexible enclosure forms a flexible wall and floor that encloses and defines a volume with an open top.
 22. A hub assembly for selectively erecting and collapsing a structure for enclosing a child comprising: a common member having a grip for lifting and lowering the common member; first and second geared members pivotally mounted to said common member so that said gears meshingly engage one another; each gear member respectively pivotally supporting one of first and second pairs of support rods whereby, when the hub assembly is lifted, free ends of said first and second pairs of support rods move toward one another through substantially equal angles due to the meshing engagement of said first and second geared members.
 23. The assembly of claim 22 wherein, when said common member is lowered, the first and second pairs of support rods move away from one another and lie in a common plane.
 24. A hub assembly for selectively erecting and collapsing a structure for enclosing a child, comprising: a common member having a grip for lifting and lowering the common member; a pair of rotatable members pivotally mounted to said common member; each rotatable member respectively pivotally supporting first and second pairs of support rods; said rotatable members each further having a blocking shoulder and a clearance shoulder; said blocking shoulders diagonally aligned and with one another and said clearance shoulders being diagonally aligned with one another; and a locking tab rotatably mounted upon said common member and being normally urged in a first direction by a biasing force causing opposing sides of said locking tab to engage said tab locking shoulders when said common member is lowered to retain said tab in a locked position; and said tab in the locked position engaging said blocking shoulders to prevent said hub assembly from being lifted.
 25. The hub assembly of claim 24 wherein said common member is unlocked by rotating said locking tab in a second direction against said biasing force enabling said opposing sides of said locking tab to move away from said locking shoulders to thereby release said common member.
 26. A hub assembly for selectively erecting and collapsing a structure for enclosing a child comprising: a common member having a grip for lifting and lowering the common member; first and second gear members pivotally mounted upon said common member; each gear member having a pair of spaced apart gears to provide a gap therebetween; each gear of one of the gear members meshing with an associated gear of the other one of said gear members; each gear member respectively pivotally supporting one first and second pairs of support rods whereby, when the hub assembly is lifted, free ends of first and second pairs of support rods move toward one another through substantially equal angles due to the meshing engagement of said first and second geared members; each first gear having a notched portion forming a transversely aligned tab locking shoulder and a blocking shoulder; each second gear having a notched portion forming a transversely aligned tab shoulder and a blocking shoulder; and a locking tab rotatably mounted upon said common member and being normally urged in a first direction by a biasing force causing opposing sides of said locking tab to engage said tab locking shoulders when said common member is lowered to retain said tab in a locked position; and said tab in the locked position engaging said blocking shoulders to prevent said hub assembly from being lifted.
 27. A hub assembly for selectively erecting and collapsing a structure comprising: a common member having a grip for lifting and lowering the common member; first and second geared members pivotally mounted upon said common member so that said gears meshingly engage one another; each gear member respectively pivotally supporting one first and second pairs of support rods whereby, when the hub assembly is lifted free ends of said first and second pairs of support rods move toward one another at a substantially equal amounts due to the meshing engagement of said first and second geared members.
 28. A hub assembly for selectively erecting and collapsing a structure for enclosing a child comprising: a common member having a grip for lifting and lowering the common member; first and second geared members pivotally mounted upon said common member so that said gears meshingly engage one another; each gear member respectively pivotally supporting one first and second pairs of support rods whereby, when the hub assembly is lifted free ends of said first and second pairs of support rods move toward one another at a substantially equal amounts due to the meshing engagement of said first and second geared members.
 29. A method for operating a hub assembly of a playard comprised of first and second gear members each comprised of a first and second spaced apart gears pivotally mounted to a common support; The first and second gears of the first member respectively meshing with a first and second gear of said second member; each first gear having a notch defining first and second transversely aligned gear and tab locking surfaces and each second gear having transversely aligned gear locking and tab clearance surfaces; and a locking tab rotatably mounted on said support, said method comprising; lowering the hub assembly to a first position to move the tab clear of said gear locking and tab clearance surfaces; and rotating said tab in a first direction to engage said tab locking surfaces and thereby prevent said tab from further rotation in said first direction, whereby said tab engages the gear blocking surfaces of said gear members to prevent lifting of said hub assembly.
 30. The method of claim 29 further comprising; rotating said tab in a second direction opposite said first direction, said tab being free to rotate in said second direction past said tab clearance surfaces and is moved to a position spaced from said first and second gears of said first and second members; and lifting said hub assembly to rotate said gear members to a collapsed position. 